Recently, an importance of developments of technologies for preventing global warming, and reducing environmental loads, such as conservation of energy resources, has rapidly increased. With such trends, attentions have been attracted to technologies for recovering and recycling waste heat, which has been regarded as useless and discarded in the conventional art. One of the technologies is an adsorption heat pump.
The adsorption heat pump is a technology for converting low quality thermal energy of 100° C. or lower into usable cooling heat by using transfer of latent heat generated when an adsorbate, such as water, and methanol, is adsorbed or desorbed on an adsorbent, such as silica gel, and activated carbon.
Many researches have been conducted on the adsorption heat pump since 1978, as energy can be recovered from various types of low temperature waste heat, because heating heat required for desorption can be relative low temperature, such as about 60° C., depending on a type of an adsorbent.
In order to achieve an adsorption heat pump having a high energy recovery efficiency, required is an adsorbent, which causes desorption with lower waste heat temperature (50° C. to 60° C.), and causes adsorption with higher cooling water temperature (25° C. to 30° C.), which means that an adsorption and desorption reaction is carried out in the relative vapor pressure range of 0.2 to 0.6 in an adsorption isotherm.
Silica gel and zeolite, which are currently often used as adsorbents for adsorption heat pumps, easily adsorb water at high temperature, because surface thereof are hydrophilic. However, the silica gel and zeolite have a problem that it is difficult to desorb the water. The reason thereof is because an adsorption amount is relative high at the relative vapor pressure of less than 0.2, and a changed amount in the aforementioned range of the relative vapor pressure is small.
As for an adsorbent other than those mentioned above, use of activated carbon has been studies. The activated carbon surface of which is hydrophobic has excellent desorption properties at low temperature, a ad has an adsorption amount of substantially 0 in the low relative vapor pressure range. Moreover, the rising of the adsorption isotherm thereof is sharp, and thus there is an advantage that a large difference in the adsorption amount can be secured. On the other hand, there is a problem that the intended performance cannot be attained with high cooling water temperature, because the adsorption and desorption reaction is carried out at the relative vapor pressure of greater than 0.6, when the activated carbon is used as it is.
According, the activated carbon has been modified for use. Examples of the modification of the activated carbon include a hydrophilic treatment of a surface of the activated carbon. For example, proposed is hydrophilic activated carbon obtained by subjecting activated carbon, which has been generated by treating an organic polymer resin with an activator agent, to an acid treatment, which is a hydrophilic treatment (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2005-288224). The acid treatment is carried out by dipping the activated carbon in nitric acid or a hydrogen peroxide aqueous solution.
However, the acid treatment has a problem that the hydrophilic treatment cannot be controlled and it is difficult to obtain an adsorbent having a desired adsorption isotherm, as the acid treatment is merely to dip the activated carbon in an acidic reagent. Even when an adsorbent having a desired adsorption isotherm is obtained, heat resistance of the adsorbent is not sufficient, and the adsorption isotherm is changed by heat. Therefore, the acid treatment cannot provide an adsorbent for adsorption heat pumps having a high energy recovery efficiency and excellent heat resistance.
Accordingly, there are currently needs for an adsorbent for adsorption heat pumps, which has a high energy recovery efficiency, and excellent heat resistance, a production method thereof, and an adsorption heat pump, which has a high energy recovery efficiency.